A radiometer is comprised of two units: a radiation receptor, which contains a "black body cavity" and a compensating cavity, or other compensting element both of which are located in a heatsink, and a controller. The radiation detector absorbs radiant energy and generates a voltage proportional to the power of the radiation received. The function of the controller is to calibrate the radiation detector and to amplify for display the voltage generated.
Since the principal use of a radiometer is to measure the sun's radiation, both units are exposed to radiation and therefore subjected to a range of ambient temperatures great enough to generate errors that prevent the radiometer from reaching its full capability of precision, which is three hundredths percent accuracy. Due to the time variability of solar radiation, there is often need to collect radiation data at specific times. It is therefore necessary for this high precision to be maintained over relatively long periods of time.
The absolute accuracy of radiation measurements in general, and solar measurements in particular, has been increasing, but the present level of accuracy is only a few tenths of a percent. Current solar and atmospheric research now demands the higher accuracy of three hundredths percent, and further demands that such higher accuracy be maintained over relatively long periods of time. This requires an improvement in the radiometer controller of at least one order of magnitude.